This invention relates to engraving and more particularly to the sensing and reproduction of patterns on photosensitive surfaces, as in the production of printing plates.
Heretofore, the essential operations in the production of modern engravings have included photography by which material assembled on the copy board is illuminated by high intensity lamps and converted to a negative. The negative is then used to expose a photo-receptive printing plate, which is either composed of or coated with a photosensitive material. Examples of such photosensitive plates have been in the past of many kinds, some adapted particularly for relief printing, while others are adapted for intaglio (gravure) printing. The present invention will fine a wide variety of applications and, as will become apparent, the type of printing plate to be produced is not limited in the present invention, but may be of any usual type. In recent years, newspapers and commercial printing of various types have resorted to photo-composition and, particularly, in the utilization of printing plate materials based on photosensitive polymeric systems. A typical process consists of the direct exposure of a photopolymer layer carried on a suitable substrate to a negative prepared in the manner previously discussed, after which the exposed polymer layer and substrate are processed to selectively remove those portions which have not been exposed to develop the photo-engraved printing plate.
In certain systems, the negative is contact printed to the plate while in others it is imaged by a suitable lens and camera apparatus. While considerable progress has been made in the art of producing printing plates, it has still been required that such plates be produced from negatives generated by photographic processes. Although capable of producing plates of high quality, such processes require materials such as negatives and chemicals, expensive camera equipment, and numerous time consuming and costly operations to accomplish.
While there have been proposals for direct production of printing plates using a laser beam or electron beam for etching the same, the systems proposed have not been satisfactory due to problems such as inherent non-linearities of the optical system used for the sensing and etching operations, resulting in low resolution and low production. Such systems have also been unduly sensitive to small vibration resulting in degradation of image quality.